The present invention relates to improvements over the dust-proof structure for a linear motion actuator with a carriage which is provided in a casing, and is linearly moved in an axial direction.
In general, a linear motion actuator is provided with a type as shown in FIGS. 6 and 7. A pair of parallel linear guides are disposed on an elongated base 101. A carriage 105 is fastened to a slider 104, which linearly moves along the guide rail 103. The carriage 105 is coupled with a ball nut 107 of a ball-and-screw mechanism 106 as a rotation-linear converting mechanism. An AC servo motor 108 drives a ball-screw shaft 109 to rotate. With rotation of the ball-screw shaft, the carriage 105 is linearly moved along the guide rail 103 in the axial direction. A workpiece W is fastened onto the driven member mounting portion 110 located on both sides of the carriage 105, by means of screws. The accurate linear motion and the accurate positioning of the work can be carried out repeatedly.
The actuator is covered with side covers 111, an upper cover 112, an end cover 113, and the like, for the purposes of improving appearance and protecting the inner accurate parts, such as the linear guides 102 and the ball-and-screw mechanism 106, from incoming dust.
The driven member mounting portion 110 of the carriage 105 must be exposed to, so slits are formed between each side cover and the upper cover 112. The slits axially extend over the entire range of the movement of the carriage 105. The slits S allows dust to enter the inside of the casing. In this respect, the dust-proof measure is imperfect.
A linear motion actuator of the type in which the slits covering the carriage movement range are covered with a movable belt is disclosed in Unexamined Japanese Utility Model Publication No. Hei. 4-60642. As shown in FIGS. 8 and 9, a carriage 121 is axially slidable within a cylinder tube 120 with an axially elongated slit S formed in one side (upper surface) thereof. The carriage 121 is coupled with a ball nut 124 receiving a screw shaft 123 of the ball-and-screw mechanism 122, and is linearly moved in the axial direction by an AC servo motor 125.
A table body 126 is protrudes above the carriage 121, and is exposed over the cylinder tube 120 through the slit S. An upper surface of the table body 126 serves as a driven member mounting portion 128 with bolt holes 127 at the four corners.
A shaft receiving hole 130 through which the screw shaft 123 passes is formed in the carriage 121, as shown in FIG. 9. A nut receiving space 131 for receiving the ball nut 124 is formed in the middle of the shaft receiving hole 130. A square groove 131a is formed in the ceiling wall of those walls defining the nut receiving space 131. The bottom of the nut receiving space 131 is open. A ball nut 124 with a square stopper 132 is placed in the nut receiving space 131 in a state that the protrusion 132 is fit to the groove 131a.
The carriage 121 having two downward extending slopes is shaped like V in cross section. A slider member (not shown) is secured to the bottom edges of the slopes of the carriage 121. In this state, the carriage 121 is disposed within the cylinder tube 120 shaped like a diamond in cross section.
The table body 126 which protrudes over the carriage 121 has a band receiving hole 136 through which the seal band 135 passes. The band receiving hole 136 has a gently upward curved band guide face 137, and opens downward. The opening of the band receiving hole is longitudinally elongated in the lower side of the table body. The seal band 135 made of a thin steel band is inserted into the band receiving hole 136 from the opening.
After the carriage 121 is assembled into the cylinder tube 120, the slit S of the upper surface of the cylinder tube 120 is covered with the seal band 135. A strip like rubber magnet is attached to the edge of the slit S. The seal band 135 is magnetically attracted by the magnet rubber, thereby improving the sealing performance by the seal band. The ends of the seal band 135 are secured to the end cap 140 and the head cap 141. The mid portion of the seal band 135 is located on the curved band guide face 137 of the carriage 121.
The AC servo motor 125 is turned forwardly or reversely, so that the screw shaft 123 is driven. Then, the ball nut 124 is moved forward or backward. In turn, the carriage 121 is moved forward or backward while being guided by the cylinder tube 120. The workpiece mounted on the driven member mounting portion 128 of the table body 126 is axially moved and stopped at a desired position.
At this time, the seal band 135 prevents dust from entering through the slit S of the cylinder tube 120. The table body 126 moves forward while pushing upward with the curved surface of the band guide face 137.
The conventional dust proof structure of the type in which the slit S of the cylinder tube 120 is sealed with the seal band 135 has a high dust proofing capability, but has the following problems.
(1) Since the seal band 135 is passed within the carriage 121, the carriage structure is complicated, and it is impossible to increase the rigidity of the carriage 121.
(2) The band receiving hole 136 extends longitudinally to pass through the central portion of the table body 126 of the carriage 121. The bolt holes 127 cannot be located in the central part of the driven member mounting portion 128 which is advantageous in securing a high rigidity. Accordingly, the bolt holes 127 must be located at the four corners of the driven member mounting portion 128. This results in increasing the size of the carriage 121.
In the case of a large linear motion actuator which transports a heavy workpiece, a high rigidity is essential in order to move the work at a high speed and to position it accurately. The carriage of the linear motion actuator is a member which couples the linear guides with the workpiece. Therefore, the carriage is the most important component in determining the rigidity of the linear motion actuator. The structure which is not capable of increasing the rigidity is not suitable for a large actuator.